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Presentation to the MacDonald College

 

The optimum slenderness of the aerodynamic body is about 3 to 4 resulting in a nacelle length of some 10 feet. That also is the length of the BKB and is required anyway to provide stable ground runs. We notice that the aft end of this nacelle - or fuselage, reaches aft of the wingtips'. It provides long enough arm, aft of the CG. to carry an effective empennage.

 

Does it mean the defeat of the flying wing concept?

 

The comparison with the SB-13 will provide some answers. Both projects aim to improve the performance of the standard 15 meter. Thus, the results measure degree of success.

 

SB-13 people have chosen to be faithful to their Nurflügler. We, in our pragmatic approach end up with a hybrid. For yaw stability and control SB-13 resorted to large, wing tip located stabilizers and rudders.

 

We have a single vertical fin, as an integral part of the T-Tail. But the directional control is accomplished solely by wing tip located small plates which deflect outwards only. These rudders were found to be very effective on the BKB providing directional control even at the low speed phase of the take-off run.

 

We feel safer without the large objects at the tips of the flexible wing - very likely invitation to flutter.

 

We tried to change the configuration of the conventional sailplane to make each component contribute to stability in pitch and in yaw.

 

The forward location of the swept back wing reduces the length of the fuselage, thus eliminating the destabilizing effect of the conventional cockpit.

 

The use of the stable airfoil and arranging for the appropriate elevon deflection made the wing stable in pitch. Its sweepback provides a degree of directional stability.

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